The present invention relates generally to a vehicle automatic transmission including a torque converter with a direct drive clutch, and more particularly to a controlling apparatus of the direct drive clutch.
Such an automatic transmission conventionally includes, besides the torque converter, and the direct drive clutch which is adapted to directly connect an input and an output member of the torque converter, at least one planetary gear unit connected with the output member of the torque converter, a plurality of frictional elements by which the power transmission path in the planetary gear unit is changed to obtain a plurality of shift positions, and hydraulic circuit means for selectively supplying oil pressure to the frictional elements based on a predetermined relation between the vehicle speed and the engine torque and for supplying the oil pressure to the direct drive clutch also.
In such an automatic transmission, the direct drive clutch is engaged only in the third speed shift position and when the vehicle speed is more than a predetermined value so as to eliminate slip in the torque converter and to improve the fuel consumption characteristic.
Conventionally, however, the direct drive clutch is controlled by hydraulic circuit means only, so that the control of the direct drive clutch depends on the shift position control. Thus, a direct drive condition can be obtained only in the third speed, so that a sufficient improvement of the fuel consumption characteristic cannot be achieved. Further, since the direct drive clutch is engaged at the time of shifting, when the vehicle is driven at a high speed, the automatic transmission produces a substantial shift shock.